This disclosure relates to a gas turbine engine, and more particularly to a background radiation measurement system.
Gas turbine engines typically include a compressor section, a combustor section and a turbine section. During operation, air is pressurized in the compressor section and is mixed with fuel and burned in the combustor section to generate hot combustion gases. The hot combustion gases are communicated through the turbine section, which extracts energy from the hot combustion gases to power the compressor section and other gas turbine engine loads.
A typical turbine section includes at least one array of turbine blades arranged circumferentially about an about an engine central longitudinal axis. The turbine blades are subject to thermal distress due to the hot combustion gases, as well as mechanical distress at high rotational speeds about an engine axis. In some instances, the turbine blades may vibrate or deflect due to thermal and mechanical stresses or cracking.
Typical stress measurement systems include a laser source and a photo-detector mounted remotely away from the engine and connected to a probe via fiber optics cables. The laser source emits a laser beam via a transmit fiber and a lens onto each of the turbine blades as the turbine blades rotate through the field-of-view of the probe. The surface of each turbine blade reflects the laser beam toward a receive lens and fiber, which communicate the light to the photo-detector which converts the light to an electrical signal and in turn triggers a timer. This time is recorded to determine a “time of arrival” of the turbine blade. The turbine blades are positioned downstream from the combustor section. Thus, the system is typically configured to filter background radiation generated by a flame (which may closely match the wave length the photo-detector expects) from the combustor in order to minimize noise, which may affect the detection of the time of arrival of the blade, vibratory modes of interest, or signal strength. Accordingly, a system configured to receive radiation from a background radiation source is desirable.